Frequently Asked Questions
What is a NIPT?
Non-invasive prenatal testing (NIPT) uses cell-free DNA (cfDNA) derived from the pregnancy to evaluate possible chromosomal conditions in a pregnancy.
NIPT is a prenatal screening test that can be performed as early as 10 weeks’ gestation using a 2 vials of blood. Prenatal diagnostic tests such as amniocentesis and CVS can diagnose the presence of chromosomal conditions. These are typically performed later in pregnancy and are associated with a small risk of pregnancy loss.
What are the differences between NT and NIPT?
A Nuchal Translucency (NT) measurement (the thickness of the fluid at the back of the baby's neck) with ultrasound when combined with a blood test and other maternal information, provides an indication of the risk factor or likelihood of a baby being born with Down syndrome.
NIPT, on the other hand, directly analyses the cell-free foetal DNA circulating in the pregnant mother's blood to detect the presence (or absence) of Down syndrome (trisomy 21) and a number of other foetal chromosomal conditions (trisomies 18 – Edwards Syndrome and 13 Patau’s Syndrome).
The detection rate for NIPT is among the highest available for this type of antenatal screening and is recommended by the International Society of Prenatal Diagnosis (ISPD) (Benn et al. Prenat Diagn. 2015 Aug;35(8):725-34).
Why from 10 weeks?
Cell-free foetal DNA (cff DNA) comes from the placenta. It is first detectable from about 4-5 weeks’ gestation and reaches the required level needed for testing by 10 weeks’ gestation in most pregnancies.
How accurate are the results?
The Warwick Evidence Systematic Review of the performance of NIPT found that the negative predictive value of NIPT was 99.9%. What does that mean? The negative predictive value (NPV) tells you how likely it is that a low probability NIPT result is correct.
So, if you get a result that shows a low probability of the conditions screened for: you can be pretty certain you do not have a fetus with any of the conditions.
In the event of NIPT results showing a high probability of the conditions screened for: the positive predictive value (PPV) varies for each condition from 81.6% for Down’s Syndrome, 49% for Patau’s Syndrome, and 37% for Edwards’ Syndrome. A high probability result does not definitively confirm the presence of one of the conditions and further testing is required.
There may be some factors which cause an inconclusive result (See Further Reading below) and a further invasive test may be required for accurate determination.
NIPT tests are extremely accurate in the detection of pregnancies where there is a high probability of Downs’ Syndrome, Patau’s Syndrome or Edwards’ syndrome.
- Up to 99% detection rate for Down's Syndrome (Trisomy 21)
- Up to 97% detection rate for Edwards Syndrome (Trisomy 18)
- Up to 94% detection rate for Patau's Syndrome (Trisomy 13)
What does that mean in real terms? The NIPT test will detect 99% of pregnancies where a high probability of Down's Syndrome is present.
The NIPT is more accurate than the first trimester combined test or second trimester quadruple test for estimating the chance or risk that the baby has Down's syndrome. The false positive rate for all trisomies is <0.1%. Conventional screening tests can miss 15% or more of trisomy 21 cases.
More information on the Warwick Evidence Systematic Review can be found here.
Who are not suitable for the NIPT?
Women who have the following are not suitable for NIPT testing:
- A history of active malignancy
- A pregnancy with fetal demise
- A pregnancy with more than 2 fetuses
- A history of bone marrow or organ transplant
- Rare maternal biological conditions may affect the accuracy of the test
- Maternal Aneuploidy
Can I find out the sex of the baby from my NIPT test?
Foetal sex is available for twin and singleton pregnancies at no extra charge and is up to 99% accurate. A study performed by The American College of Medical Genetics in 2016 correctly identified the gender in 786 of 787 cases.
In the case of a twin pregnancy only - if a male result was generated, we would not be able to tell if it was one or both twins that were male.
Can I have this with a twin pregnancy?
The NIPT test can be performed on twin pregnancies but not additional (ie triplets or higher) and only when both foetuses are ongoing. The NIPT test in twins was based on viable twin pregnancies.
If a male result was generated, we would not be able to tell if it was one or both twins that were male.
In cases of a demised co-twin, “vanishing twin”, or an empty gestational sac the test becomes invalid. A demised twin may in fact produce more cell-free DNA than the live twin and skew the results. For these reasons we do not recommend cell-free DNA testing in the case of demised twin.
Can I have this with an IVF pregnancy?
Yes. This test is appropriate for IVF pregnancies.
How long do I wait for the blood test results?
The results should be received 7-10 working days following your blood sample being taken.
How will I receive my test results?
If your results are found to show low probability – an email will be sent to the email address confirmed with you at the time of your appointment.
In the event of your results showing a high probability – you will be called on the telephone number confirmed with you at the time of your appointment by a member of our specialist team from Head Office.
What if my results indicate a baby with Down's Syndrome?
There are three possible results from NIPT for Down syndrome:
A high chance of the foetus being affected by Down syndrome. An invasive test is required to confirm the result.
A low chance of the foetus being affected by Down syndrome.
Inconclusive results happen in up to 4% of cases. This is usually because the proportion of foetal DNA present in the sample is not high enough to give an accurate result. NIPT may be repeated with the hope that the cfDNA levels will have increased due to the increased gestation. NIPT detection rate is around 98% of all babies with Down, Edwards and Patau syndromes.
Twin Pregnancy - What if my results indicate a high probability of Downs Syndrome?
A high probability test result will apply to at least one fetus:
- Male test results apply to one or both fetuses
- Female test results apply to both fetuses
What if the sample fails?
Statistically there is a 3 to 4% failure rate that there is not enough cell free DNA in the blood sample to analyse. In this event a new sample will need to be taken again at no extra cost.
What if I have a high BMI?
The relative proportion of cell-free fetal DNA is reduced in women with a high BMI as they have more of their own cell-free DNA circulating in their blood.
This may increase the chance of getting an inconclusive result.
Can the sex chromosomes be analysed for anomalies?
No. We do not undertake Sex Chromosome Aneuploidy screening to evaluate the X and Y chromosomes. The reason for not offering this is due to the lack of research currently available into the accuracy and detection rates of this aspect of the NIPT test.
Other reasons for not offering this include:
- A 1-in-360 chance a high-probability result is a false positive
- A high incidence of maternal and foetal mosaicism - when maternal and foetal DNA has a mixture of euploid (cells with correct number of chromosomes) and aneuploid (cells with an incorrect number of chromosomes). Unfortunately, there is no test for mosaicism.
- Foetal mosaicism can account for up to 50% of Sex Chromosome Aneuploidy cases.
- A test with an increased risk for SCA may actually be mosaic
- It can make the test less accurate
- Known age-related loss of X Chromosomes in normal women can make the test less accurate (from 16 to 65 the loss rate ranges from 0.07%-7.3%)
- 90% of women with XXX are not aware they have a third chromosome - presence of an unknown maternal sex chromosome aneuploidy affects the validity of the SCA.
It is for these reasons that we do not offer Sex Chromosome Aneuploidy as an option on NIPT.
Do you test for Microdeletions?
A microdeletion is the absence of a small piece of chromosome and is named by the area of the chromosome that is absent. The Harmony test can, for an additional cost, look for 22q11.2microdeletion, the most common genetic cause of intellectual disability and heart defects after Down syndrome. However, currently due to a lack of research into the reliability of this test Ultrasound Direct are not offering this as an additional option at this present time.
The fetal cfDNA percentage on my NIPT results is X amount, is this a normal amount?
Generally, the fetal fraction must be above 4 percent, which typically occurs around the tenth week of pregnancy. Low fetal fractions can lead to an inability to perform the NIPT test or render a false negative result. Reasons for low fetal fractions include testing too early in the pregnancy, sampling errors, maternal obesity, and fetal abnormality.
I have received my NIPT results and it states “review results with patients”, is something wrong?
This is a generic message on all Harmony test results. Subject to the results: we will only call you if a ‘high probability’ outcome is recorded, otherwise all ‘low probability’ reports will be sent via email.
Are your sonographers qualified?
Yes. All our sonographers are fully trained and qualified to perform ultrasound scans and many of them also work in the NHS locally. Scans with Ultrasound Direct will always be performed by a qualified professional whose primary interest is your health. All our sonographers take care to follow the latest safety guidelines and are registered with the HCPC. We’re also registered with the independent regulator the Care Quality Commission to ensure the highest standards possible.
What if I get bad news during my scan?
In the event of unexpected findings: we will offer clear advice on the next steps available to you and will offer to contact the local hospital on your behalf.
Should you receive bad news in your scan you are welcome to take time in private in our clinics to process the news and gather your thoughts before leaving: we never want you to feel rushed.
Are children welcome in the scan room?
Yes! The number of guests you can bring in for a scan is listed with the scan on our website. We only ask that any guests are well behaved: that includes children, excited partners and new grandparents!